Optimization of dechlorination conditions and reaction kinetics of aluminum gel

doi:10.19965/j.cnki.iwt.2025-0420

Abstract

Abstract:

A new aluminum gel dechlorinating agent was used to replace sodium meta-aluminate in the traditional Friedel's salt precipitation method, and the effects of chemical dosage, reaction time, reaction temperature, initial Cl^- concentration, and coexisting SO₄ ^2- concentration on the dechlorination effect were investigated, and the mechanism of the influence of temperature on the reaction behavior was revealed through the kinetic study of the reaction at different temperatures. The results showed that when n(Ca²⁺)∶n(Al³⁺) was 3 and n(Al³⁺)∶n(Cl^-) was 1, the reaction time was 60 min, the reaction temperature was 20-40 ℃, and the initial Cl^- concentration was 200 mmol/L, the Cl^- removal rate and Al utilization rate were both maintained at about 60%. In addition to the main product Friedel's salt(Ca₄Al₂(OH)₁₂Cl₂), the by-products tricalcium aluminate(Ca₃Al₂(OH)₁₂) and Ca(OH)₂ were detected in the reaction precipitates. Appropriate elevation of the temperature not only improves the reaction rate, but also enhances the efficiency of the dechlorination reaction. However, excessively high temperature increases the tendency for side reactions to occur, leading to a phase transition of Ca₄Al₂(OH)₁₂Cl₂ to produce Ca₃Al₂(OH)₁₂, which results in a significant decrease in the Cl^- removal rate.

Key words: aluminum gel, dechlorination, kinetics

摘要：

采用新型铝凝胶除氯剂代替传统弗氏盐沉淀法中的偏铝酸钠，考察了药剂投加量、反应时间、反应温度、初始Cl^-浓度、共存SO₄ ^2-浓度对除氯效果的影响，通过不同温度下的反应动力学研究，揭示温度对反应行为的影响机制。结果表明，当n（Ca²⁺）∶n（Al³⁺）为3，n（Al³⁺）∶n（Cl^-）为1，反应时间为60 min，反应温度为20~40 ℃，初始Cl^-浓度为200 mmol/L时，Cl^-去除率和Al的利用率均维持在60%左右。反应沉淀物中除主产物弗氏盐〔Ca₄Al₂（OH）₁₂Cl₂〕，还检测到副产物铝酸三钙〔Ca₃Al₂（OH）₁₂〕和Ca（OH）₂。适当升高温度不仅能够提高反应速率，还能提高除氯反应效率，但温度过高会使副反应发生倾向程度增大，导致Ca₄Al₂（OH）₁₂Cl₂发生相转变，生成Ca₃Al₂（OH）₁₂，从而使Cl^-去除率显著下降。

关键词: 铝凝胶, 除氯, 动力学

CLC Number:

X703.1

Yiwei ZHANG, Mingquan CHENG, Yuchen XU, Yitao MA, Zhenlong LIAO, Xiaodan ZHAO, Qing XIA. Optimization of dechlorination conditions and reaction kinetics of aluminum gel[J]. Industrial Water Treatment, 2026, 46(4): 94-102.

张亦伟, 程明权, 许宇辰, 马翊滔, 廖振龙, 赵晓丹, 夏庆. 铝凝胶除氯条件优化及反应动力学研究[J]. 工业水处理, 2026, 46(4): 94-102.

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URL: https://gyscl.magtechjournal.com/EN/10.19965/j.cnki.iwt.2025-0420

https://gyscl.magtechjournal.com/EN/Y2026/V46/I4/94

Figures/Tables 14

Fig.1 The effect of n（Ca²⁺）∶n（Al³⁺） on Cl⁻ removal efficiency

Fig.2 The effect of reaction time on Cl⁻ removal efficiency of aluminum gel

Fig.3 The effect of reaction temperature on Cl⁻ removal efficiency of aluminum gel

Fig.4 Variation of chloride-removing precipitates under different reaction temperatures

Table 1 Compositional proportions of chloride-removing precipitates under different reaction temperatures

温度/℃	Ca₄Al₂（OH）₁₂Cl₂占比/%	Ca₃Al₂（OH）₁₂占比/%	Ca（OH）₂占比/%
10	35.8	37.6	26.6
20	38.9	42.8	18.3
50	35.2	46.3	18.5
60	29.8	51.5	18.7
70	22.4	58.7	18.8
80	20.2	59.4	20.4

Fig.5 The effect of initial Cl^- concentration on Cl⁻ removal efficiency of aluminum gel

Fig.6 The effect of coexisting SO₄ ^2- concentration on Cl⁻ removal efficiency of aluminum gel

Fig.7 Variation of Cl⁻ concentration with reaction time

Fig.8 Pseudo-second-order reaction kinetics at different temperatures

Fig.9 Variation of Ca²⁺ and Al³⁺ concentrations with reaction time

Fig.10 Variation of Cl⁻ concentration with reaction time

Fig.11 Fitting of the linear equation for pseudo-zero-order kinetic model

Fig.12 Variation of Ca²⁺ and Al³⁺ concentrations with reaction time in the chloride removal reaction

Fig.13 Solid-phase kinetics at different reaction temperatures

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